Lately the trend to implement higher functions and a higher degree of integration is progressing, and it is becoming necessary to integrate various functions on one chip. Some of these electronic integrated circuits are used for detecting or correcting the duty ratio (ratio of L or H in one cycle) of a signal using a multi-phase clock.
A multi-phase clock can be generated by disposing a ring type oscillator which forms a ring type loop of multi-stage amplification circuits, and/or disposing a dividing circuit in a subsequent stage of the clock source. In this configuration, however, the generated multi-phase clock may deviate from an ideal phase relationship because of the dispersion of characteristics or the like in such a device as a transistor on a circuit.
Therefore the challenges in such an electronic integrated circuit are to search for a cause of the shift of the phase relationship by accurately detecting the phase difference and generating a desired phase difference.
FIG. 19 and FIG. 20 are diagrams depicting an example of prior art for detecting a phase difference.
For example, a case of detecting a phase difference of two measurement target clocks, as shown in FIG. 19A, is considered. In this case, as FIG. 19B shows, the phase difference can be detected by using a reference clock having a sufficiently faster frequency (or shorter cycles) than the frequencies of the measurement target clocks, and counting the clock count of the reference clock (e.g. beginning of Non-patent Document 1).
On the other hand, as shown in FIG. 20, the phase difference of the two measurement target clocks can also be detected by mixing the reference clock and the two measurement target clocks respectively by mixers 151 and 152, adding the results by an adder 154, and detecting this output signal by such an external measurement device as an oscilloscope.
Non-patent Document 1: Precise All Digital Frequency Detector for High Frequency Signals, Martin T. Hill and Antonio Cantoni, IEEE Transactions on Communications, Vol. 48, No. 11, November 2000, pp. 1937 to 1944
If a high-speed reference clock is used, however, such a circuit as a counter, to count the clock count, must also be operated at high-speed. Therefore the use of a high-speed reference clock often becomes an impractical demand, and with which the phase difference of the input clocks cannot be detected accurately.
Also the external measurement device that is used for detecting the output signal cannot be used for application to detect the phase difference by the phase difference detector integrated in the semiconductor. This requires an additional cost.